Oxygen production



Patented July 25, 1950 Henry J. Ogorzaly, Summit,

Standard Oil Develo ration of-Delaware N. 1., assignor to pment Compan a corpo-.

Application June 18, 1946, Serial No. 677,503

3 Claims. (01. 62-1755) The present invention is concerned with an improved process for the production of oxygen from air. It is more particularly concerned with an arrangement and sequence of heat exchanging stages by which improved efficiency in the exchange of heat is realized. In accordance with the present invention at least one heat exchange medium is circulated between the incoming feed air stream and the outgoing product stream un; der conditions to secure direct contact between .the circulating heat exchange medium and the air stream and the product stream. The preferred modification of the present invention comprises employing a plurality of heat exchanging mediums for transferring refrigeration from the product stream to the feed 'air'stream and simultaneously controlling the critical temperature range over which the particular selected medium is used. By operating in accordance with the present invention. unexpected desirable results are secured. and the emciency of the operation is materially improved.

It is well known in the art to manufacture oxygen and nitrogen from air. In these Processes, the air is liquified and fractionated to secure products having the desired high quality and purity. Since the operation is conducted at very low temperatures it is obvious that one major problem encountered, is the efiicient transfer of refrigeration from-one stream to the other. Various proposals and suggestions have been made water vapor to revaporize or sublimate and they are then carried out with the reaction products.

I S nce the outgoing nitrogen product stream is colder, then the chilled air stream from which the ice and carbon dioxide is condensed, thesuccess of the reversible exchanger depends upon a balance of the differences in the respective temperatures and pressures. If carbon dioxide snow is to' be revaporized there exists a critical maximum temperature difierence which must not be exceeded, otherwise sublimation of the carbon dioxide snow will not be secured even at the lower pressure of the reversing streams.

I have now discovered an improved process for transferring refrigeration from the chilled product streams to'the incoming feed air stream. In accordance with my invention I utilize at least one liquid heat transfer medium, preferably a plurality of liquid heat transfer mediums to transfer refrigeration between the respective streams in an eflicient manner. The process of my invention may be readily understood by reffor the efficient transfer of heat from the incoming air stream to the chilled outgoing product stream. In the design of suitable heat exchange equipment, the problem is complicated by the fact that in cooling air to the desired temperature, water vapor freezes out in the form of ice, and carbon dioxide in the form of carbon dioxide snow. Thus in a relatively short period of time the heat exchange equipment is plugged due to the ice and ca'rbon dioxide snow.

One process that is currently used to overcome the plugging of exchangers or accumulators is to use reversible exchangers or accumulators. In this process the incoming air stream is compressed to a pressure in the range from about 4 to about- 8 atmospheres and higher andis caused to countercurrently contact the outgoing cold product streams. The cold product streams are usually at lower pressures, generally around atmospheric pressure. After the streams have flowed in this manner for a period of time, and the ice and snow plugging has not as yet reached a critical maximum, the respective streams are reversed. This causes the carbon dioxide and the erence to theattached drawings illustrating modifications of the same.

Figure 1 illustrates a modification of my invention wherein the refrigeration is removed from the chilled nitrogen product stream by direct contactand wherein only one stage of direct contact is employed to remove refrigeration from the oxygen product stream. Figure 2 illustrates a modification of my invention wherein direct contact is used to remove the refrigeration from both the oxygen and the nitrogen product streams.

The incoming feed air stream is introduced into the system by means of line 5, compressed to the desired degree in compressor 6 and introduced into the bottom of air cooling zone- I. The air flows upwardly through air cooling zone land is removed overhead by means of 'line 1.

The major portion of the air is introduced into the bottom of air cooling Z ne 2; The air stream is removed from the top of zone 2 by means of line 8 and is introduced into an initial intermediate cooling zone.9. Zone 9 is operated under conditions to supply necessary auxiliary refrigeration so that the temperature difference between the entering air stream and the issuing. product streams isreduced to below the critical .value for sublimation of carbon dioxide snow into the product streams. An external refrigerant is employed to abstract heat in zone 9. I

v The air is removed'frcm zone 9 by means of line H and introduced intothe bottom of air cooling zone 3. The air stream is removed overexchanging zone 22. through zone 22 and is removed overhead by aura-n7 head from air cooling zone 8 by means of line I! and passed through a secondary intermediate cooling zone II. The air is withdrawn from the secondary cooling zone It by means of line I and introduced into the bottom of air cooling zone 4. The air is removed overhead from air cooling zone 4 by means of line H and passed through air fractionating equipment which, for the purpose of simplicity, is not shown on the drawings. The air fractionating equipment may comprise any suitable means for segregating the various constituents of the air stream into gaseous oxygen and nitrogen.

The cold fractionated products comprising gaseous oxygen and gaseous nitrogen are removed from the fractionating means and handled in a manner as hereinafter described. The cold gaseous nitrogen product stream removed from the fractionating means is introduced into the bottom of nitrogen heat exchanging zone 20 by means of line i3. The nitrogen flows upwardly through heat exchanging zone 23, is removed overhead by means of line 26 and is introduced into the bottom of heat exchanging zone 2 i. nitrogen is removed overhead from nitrogen heat exchanging zone 2| by means of line 21 and introduced into the bottom of nitrogen heat Nitrogen flows upwardly means of line 22 and introduced into the bottom of nitrogen heat exchanging zone 23. The warm nitrogen stream is removed from nitrogen heat exchanging zone 23 by means of line 29 and removed from the system. This stream may be handled in any manner desirable or further processed.

In accordance with my invention, I circulate a heat transfer medium between the respective air cooling zones l, 2, 3 and 4 and the nitrogen heat exchanging zones 23, 22, 2i and 20 respectively, under conditions whereby direct contact between the respective streams and the circulating heat exchange medium is secured. In accordance with my invention, the heat transfer me'diumis introduced into the top of air cooling zone 4 by means of line 20. The liquid medium flows downwardly in air cooling zone 4 and countercurrently contacts the upfiowing air stream. The liquid medium is withdrawn from the bottom of heat exchanging zone "by means of line 32 and recirculated to the top of air cooling zone 4 by means of pump 33.

A liquid heat transfer medium having characteristics diflerent from that utilized with respect to zones 4 and 20 is introduced into the top of air cooling zone 3 by means of line 34, This liquid stream flows downwardly through air cooling zone 3 and countercurrently contacts the upiiowing air stream under conditions whereby the air stream is cooled and the liquid stream is warmed. The liquid heat transfer medium is re-' The moved from the bottom of air cooling zone 3 by contacts the upflowing nitrogen stream which has been removed from zone 24 and introduced into the bottom of zone 2i. In this zone the liquid heat transfer medium is chilled while the vaporous nitrogen stream is warmed. The chilled liquid heat transfer medium'is removed from the bottom of heat exchanging zone 2i by means of line 4! and introduced into the top of air cooling' zone 3 by means of pump 44 and Q4;

A liquid heat transfer medium different from that used with respect to zones 2, 4, 2i and 2|! is introduced into the top of air cooling zone 2 by means of line 41. This liquid medium flows downwardly through air cooling zone 2 and countercurrently contacts th upilowing air stream under conditions to cool the air stream, whereby the liquid heat transfer medium is warmed. The warm liquid stream is removed from the bottom of air cooling zone 2 by means of line 42 and introduced into the top of nitrogen heat exchanging zone 22. In zone 22 the liquid medium flows downwardly and contacts the upflowing nitrogen stream under conditions to chill the liquid stream and to warm the nitrogen stream. The chilled liquid stream is removed from zone 22 by means of line 45 and recycled to the top of zone 2 by means of pump it.

In a similar manner a heat transfer medium which differs from that used with respect to zones 2, 3, 4, 22, ii and 2|] is introduced into the top of air cooling zone i by means of line ii. The liquid stream flows downwardly through air cooling zone I and countercurrentlyeontacts the upiiowins air stream under conditions to cool the air stream and to warm the downflowing liquid stream. The warm liquid heat transfer medium is withdrawn from the bottom of air cooling zone i by means of line 52 and introduced into the top of nitrogen heat exchanging zone 23. The liquid medium flows downwardly through nitrogen heat exchanging zone 22 under conditions to countercurrently contact the upiiowing nitrogen gases. The liquid stream is chilled while the nitrogen stream is warmed. The liquid stream is removed from the bottom of heat exchanging zone 23 by means of line 33 and returned to the top of air filing zone i by means of pumping means 54 and In accordance with a preferred modification of my invention I prefer to-split the incoming air feed stream which is removed overhead from air cooling zone i by means of line 1 into two segregated portions. The major portion of the air stream flows through air cooling zones 2, 3, and 4 in a manner as described. The other segregated portion is introduced into heat exchanger II by means of line it. This stream flows serially through heat exchangers in, fl, and i2 and also through auxiliary intermediate cooling zones 3 and M. The stream is withdrawn from exchanger it by means of line 58 and introduced into. the initial intermediate cooling zone 9. A minor portion of the air stream leaving zone 9 is segregated by means of line 200 and introduced into exchanger ii. The air stream leaving exchanger is introduced into secondary intermediate cooling zone It by means of line 51. A minor portion of the air stream leaving zone It is segregated by means of line 2lll and introduced into exchanger i2. The stream leaving exchanger l2 by means of line 52 is combined with the air stream removed from air cooling zone 4 by means of line it and passed to the fractionating means. The oxygen product removed from the fractionating means, is passed countercurrentlyto the air streams through exchangers ill, ii and II. The oxygen product is introduced into exchangers i2, i i and it by means of lines ti 32 and 23 respectively. It is to be understood that provision is made for periodically alternating the flow paths of oxygen and air in heat exchanging zones ll, ii and I2 so that ice and carbon dioxide snow deposited from the air in these exchangers sublimated into the oxygen duced into the bottom of an oxygen heat exchanging zone 24. The oxygen flows upwardly through heat exchanging zone 24 and contacts a downflowing liquid heat exchange medium which is introduced into the top of heat exchanging zone 24 by means of line 33. This liquid heat 1 exchange medium which is introduced into the top of zone 24 is segregated from the main stream.

which is withdrawn from air cooling zone I by means of line 52. This segregated portion 01' the liquid heat exchange medium. is removed from the bottom of oxygen heat exchange'zone 24 by means of line 65 and returned with the main stream to the top of air cooling zone I bymeans of line 5I. The oxygen product is removed overhead from heat exchanging zone 24 by means of line 61, removed from the system and handled in any manner desirable."

Another modification of my invention is illustrated by Figure 2. The air stream is introduced into the system by means of line I0 and compressed by compressing means II; The air is 1 introduced into the bottom of air cooling'zone 30, removed overhead from zone and introduced into the bottom of air cooling zone 3| by means of line I2. The air stream flows upwardly through zone 3|, is removed overhead by means of line 13, passed through initial intermediate cooling-zone I50 and introduced into the bottoni of air cooling zone 32. In a similar manner the air-stream flows upwardly through air cooling zone 32, is removed overhead from zone 32 bymeans of line 14, is passed through secondary intermediate cooling zone I5I wherein it-is cooled slightly and introduced into the bottom of air cooling zone 33. The chilled air stream is removed-overhead from air cooling zone 33' by means of line I5 and passed to iractionating means. The fractionatingmeans are not shown and may comprise any suitable means for fractionating the chilled air stream into the respective products, oxygen and nitrogen.

The. nitrogen stream is removed from the air fractionatin'g equipment by means of line It'and introduced into the bottom of nitrogen heat exchanging zone 33. The nitrogen stream flows upr wardly through'zone 38 and is removed overhead by means of line 11. This stream is introduced into the bottom of nitrogen heat exchanging zone 31 by means of line 11 and removed overhead from this zone by means of line I8. Thenitrogen stream is passed into the bottom of nitrogen heat exchanging zone 36 by means of line I0. This stream flows upwardly'through nitrogen heat exchanging zone 36 and is removed overhead by means of line I9 and introduced into the bottom ofnitrogen heat exchanging zone a 35. The nitrogen stream flows upwardly through heat exchanging zone 35 and is removed overhead by means ofline 30 and passed from the system.

This stream may be handled in any manner de-- sirable or further processed;

The oxygen stream is removed from the fracoxygen flows upwardly through zone 42, is re-'. moved overhead by means ofline- 33 and passed means of i handled 'in anymanner desirable.

In accordance with my invention-I introduce the heat transfer medium into the too of zone 33 by means of line- 30. This liquid stream flows downwardly through zone 33 and contacts the upiiowing air stream under conditions, to chill the air stream and to warm the liquid transfer medium stream. The liquid transfer medium stream is withdrawn from the bottom of zone 33 by means of line 3| and segregated into two portions. One portion is introduced intothe top of nitrogen heat exchanging zone'38 bymeans of line 92 while the other portion is introduced into the top of oxygen, heat exchanging zone 43 by means of line 03. These streams flow downwardly through zones 38 and 43 and contact up-' flowing nitrogen andoxygen streams respectively, under conditions to warm the oxygen and nitrogen streams and under conditions to cool the liquid downflowing medium, The liquid streams are withdrawn from thebottom of zones 38 and 43 by means of lines 34 and 95 respectively, combined, and recycled to the top of air cooling zone 33 by pumping means 06.

A heat transfer medium difierent from that employed in zone 33 is introduced into the top of air cooling zone 32 by means of line I00. This stream flows downwardly through zone 32 and contacts the upflowing air stream under condidowniiowing liquid stream. This'stream is removed from the bottom of zone 32 by means of line 'IOI, segregated into two portions, one portion of which is introduced into zone 31 by means of line I0 2'while the other portion is introduced into the top of oxygen heat exchanging zone 42 by means of line I03. These streams flow down-- wardly through nitrogen heat exchanging zone 31 and oxygen heat exchanging zone 42 and contact the upflowing nitrogen'and oxygen streams respectively under conditions towarm .the upflowing streams and under conditions to cool the downflowing heat transfer medium streams. Thesestreams are. removed from zones 31 and 42 by means of lines I04 and I05 respectively. The

streams are combined and recycled to the topofv downwardly through air cooling zone 3I under conditions to contact the upflowing air stream.

The air streamis cooled and removed as described while the liquid stream is warmed. The liquid stream is removed from the bottom of zone 3| by means of line I II and segregated into two portions. One portion is'introduced into the top of nitrogen heat exchanging zone 36v by meanscf line- II2 while the'other portion is introduced into-the top of oxygen heat exchanging zone '4I by meansof line I I3; These streams fiow. downwardly through zones 36 and 4| andcontact the upiiowing oxygen stream and the upilowing nitrogen stream. The upflowing oxygen and nitrogen ofaircoolin'gzoneli by streams are removed from the bottomof zonesil and by means oflines Ill and! respectively. Thestreams are combined and recycled to the top pumping means Ill and line Ill. I

A liquid heat transfer medium different from that employed with respect to'zones Ii, 82, 88, II, ll, 81, If, 38 and 43 is introduced into the top of air cooling zone 3| bymeans of line III. This stream flows downwardly through air cooling zone SI and contacts the upilowing gas stream which is introduced by means of line I l.v The air stream is cooled while the downi'iowing liquid stream is warmed. The liquid stream is removed from the bottom of zone 80 by means of line iii. This stream is segregated into two portions. One portion is introduced into the top of nitrogen heat exchanging zone 3| by means of line III while the other portion is introduced into the top of -oxygen heat exchanging zone II by means of to the top of air cooling zone II by pumping means.

I" and line I.

The major portion oiithe water and the carbon dioxide content of the incoming air is deposited within the liquid contact towers I, 2, 3 and 4 of Figure 1 and zones 36, SI, 32 and a of Figure 2. The solubility and vapor pressure oi these impurities in the circulating heat transfer mediums are sum'cient so that they remain in solution anddo not interfere with the liquid circulation, and are sublimated from solution into the issuing products, due to the difference in pressure, at a rate which balances their rate of introduction into the system. In the process outlined and illustrated by Figure l, approximately of the inlet air stream is cooled by product oxygen principally in exchangers II, II and i2 and in this case provision is made for periodic alternation of the paths of oxygen and air ilow to permit sublimation into the oxygen stream of solidified impurities deposited from this portion of the entering air. Substantially no impurities are deposited in the initial intermediate cooler, l in Figure 1 and iill in Figure 2, since this cooling is supplied at a temperature level between the points where the water vapor in the entering air is substantially completely deposited and the point where carbon dioxide snow deposition begins. A small amount of carbon dioxide deposi.. tion is encountered in the secondary intermediate cooling zone, It in Figure 1 and Iii inFigure 2, and this is removed by providing these exchangers induplicate and purging periodically with low tween the liquid medium and the oxygen and nitrogen product streams. 'A preferred modification of my,-invention-is to utilize direct contact between the transfer medium and the nitrogen and a maior portion of the incoming air stream in a plurality of stages and to use direct contact between the liquid medium, the oxygen stream sang the total air stream in the warmest stage In accordance with my invention I employ particularly selected heat transfer mediums which are utilized with respect to the critical range of temperature at which the transfer of refrigeration is beingconducted. In'accordance with the invention the liquid heat transfer medium under the conditions of operation-should not have a vapor pressure exceeding about 20 millimeters of me In general I prefer that the vapor pressure of the liquid heat transfer medium at the highest temperature of use be below about 5 millimeters of mercury, preferably below about 1 millimeter. It is also desirable that the,particular heat transfer medium employed with respect to the critical temperature of operation have a viscosity not exceeding about 50 centipoises, preferably below about 15 centipoises. The liquid heat transfer medium must have a freezing point above the lowest temperature at which the transfer of refrigeration is being conducted. Thus my heat transfer mediums are selected from the class of materials which, under the conditions of temperature of operations at which the heat transfer or refrigeration transfer is being conducted, have a vapor pressure below about 20 millimeters, preferably below about 5 millimeters, and have a viscosity in the range of below about 50 centipoises and do not freeze at the temperatm-e of operations.

The method of securing desired contact between the upfiowing and downflowing streams may be widely varied. The towers or contacting units may comprise packed towers, pierced plates, distributing plates or other contacting means employed in countercurrently contacting operations.

Although Figure 2 illustrates a modification of my invention in which both the product streams contact a stream of liquid heat transfer medium, which stream is subsequently recycled to the incoming air stream for direct contact, it is to be understood that different mediums may be used. with respect to the oxygen and nitrogen streams. It may be particularly desirable to use diflerent mediums for directly contacting oxygen and nitrogen in the same temperature range. Under a modified processsuch as this, air cooling zones 3|, Ii, 32 and I! may comprise a series of parallel zones. If this modification of my invention be carried out, air cooling zone I! would comprise two zones. A liquid heat transfer medium would circulate through one and the nitrogen zone, while a different heat transfer medium would circulate through the other zone and the oxygen heat exchanging zone. i

In accordance with the preferred modifications of my invention I operate in a manner as illustrated by Figure 1. At the coldest temperature I employ as the circulating medium. preferably liquid propane. Other materials, as for example, propylene or 3emethyl butene-l are also satisfactory. The operating temperature range in this zone when employing these mediums should preferably be from about -240 F. to about --2 F. In the next coldest zone I preferably employ as a liquid 'heattransfer medium, isopentane. Other satisfactory liquid heat transfer mediums used in this zone comprise isoamylene or 2-methyl pentane. The operating temperature range when employing these mediums should preferably be in the range from about 160 F. to about 250 F.

In the zones operated at temperatures above those employed inthe isopentane zone I preferably employ as a liquid heat transfer medium ethyl alcohol. Other suitable materials for this zone comprise isobutyl or isoamyl alcohol, ethyl or methyl cyclopentane, ethyl ether, butyl aldehyde and propyl benzene. If slightly higher temperatures in the cold end of the towers be employed, ethyl benzene or toluene could be utilized. The operating temperature range when employing these mediums is preferably in the range from about 35 F. to about -175 F.

In the warmest zone I preferably employ a calcium chloride brine solution of about 30% calcium chloride. Other suitable materials for example, comprise chlorbenzene, or water solutions of glycerin and ethylene glycol. The operating temperature range when employing these mediums should preferably be in the range from about 30 F. to about +100 F.

When operating as described and illustrated by Figure l, the temperatures throughout my system 25 are as follows:

one of said air contacting zones at a level below the solidification point of water and CO2. deposited from the air by chilling; withdrawing the heat transfer mediums carrying deposited water and CO: from the air contacting zones and recirculating said mediums to said first mentioned zones.

2. Process in accordance with claim 1 in which propane is used in the initial zone, isopentane .in the second zone, ethyl alcohol in the third zone and calcium chloride brine in the warmest zone.

3. In a process for the manufacture of oxygen and nitrogen from air wherein liquid air is fractionated in fractionating equipment, the improvement which comprises segregating the chilled nitrogen product stream and countercurrently directly contacting said stream in a plurality of zones with liquid heat transfer mediums, withfrom the respective zones and contacting the incoming air stream in a plurality of zones directly with the liquid heat transfer mediums withdrawn from the preceding zones, controlling the temperature in at least one of said air contacting zones at a level below the solidification point of Air, F. Liquid heat transfer, Medium T.

In Out Name In Out Air Cooling Zone 1 100 -32 Brine -37 +89 Air Cooling Zone 2 -32 l55 Ethyl Aleohol 161 37 Initial Intermediate 0,00 9 l55 164 Air Cooling Zone 3 164 240 Isopentane --244 I61 Secondary Intermediate Cooling Zone 16 -240 -243 Air Cooling Zone 4 -243 -276 Propane -379 -246 Oxygen, F. Medium F. Oxygen In Out Name In Out Heat Exchange Zone 24 43 +78 Brine +89 37 Exchanger l0 -l09 43 I Exchanger ll 247 169 Exchanger l2 -296 -247 Nitrogen, "1 Medium F.

Nitrogen In Out Name In Out Heat Exchange Zone 20 Heat Exchange Zone 21. Heat Exchange Zone 22.. Heat Exchange Zone 2! The process of my invention is not to be limited by any theory as to mode of operation but only in and by the following claims in which it is desired to claim all novelty insofar as the prior art permits.

I claim:

1. In a process for the manufacture of oxygen and nitrogen from air wherein liquid air is fractionated in fractionating equipment, the improvement which comprises segregating the chilled nitrogen product stream and countercurrently directly contacting said stream in four zones with liquid heat transfer mediums, withdrawing the respective heat transfer mediums from the respective zones and contacting the incoming air' stream in four zones directly with the liquid heat transfer mediums withdrawn from the preceding zones. controlling the temperature in at least HENRY-J. OGORZALY.

REFERENCES CITED The following references are of record in the 00 named zones.

05 file of this patent:

unrrnn s'ra'ras mm Number Name Date 1,681,928 Bell Aug. 28, 1928 1,724,513 Pollitser Aug. 13, 1929 1,741,567 Heston Dec. 31, 1939 1,905,185 Morris Apr. 25, 1933 2,141,997 Linde et al. Dec. 27, 1938 3,380,468 Brown "cum"..- Oct. 17, 1944 drawing the respective heat transfer mediums 

3. IN A PROCESS FOR THE MANUFACTURE OF OXYGEN AND NOTROGEN FROM AIR WHEREIN LIQUID AIR IS FRACTIONATED IN FRACTIONATING EQUIPMENT, THE IMPROVEMENT WHICH COMPRISES SEGREGATING THE CHILLED NITROGEN PRODUCT STREAM AND COUNTERCURRENTLY DIRECTLY CONTACTING SAID STREAM IN A PLURALITY OF ZONES WITH LIQUID HEAT TRANSFER MEDIUMS, WITHDRAWING THE RESPECTIVE HEAT TRANSFER MEDIUMS FROM THE RESPECTIVE ZONES AND CONTACTING THE INCOMING AIR STREAM IN A PLURALITY OF ZONES DIRECTLY WITH THE LIQUID HEAT TRANSFER MEDIUMS WITHDRAWN FROM THE PRECEDING ZONES, CONTROLLING THE TEMPERATURE IN AT LEAST ONE OF SAID AIR CONTACTING ZONES AT A LEVEL BELOW THE SOLIDIFICATION POINT OF WATER AND CO2 DEPOSITED FROM THE AIR BY CHILLING, WITHDRAWING THE HEAT TRANSFER MEDIUMS CARRYING DEPOSITED WATER AND CO2 FROM THE AIR CONTACTING ZONES AND RECIRCULATING SAID MEDIUMS TO SAID FIRST NAMED ZONES. 